The invention relates to a card flat bar for a carding machine, which card flat bar comprises a carrier element with a clothing support part, and two end head parts associated with the carrier element.
In a known card top bar, the carrier element and the end head parts form at least three assembled components, and the end head parts comprise at least one sliding-contact region, which is in contact with the slideway, and at least one fixing region, which is fixed to the carrier element and at the same time holds the sliding-contact region.
Modern card flat bars are extruded from aluminium. In practice, the extruded card flat bar is cut to length and finished, for example, to a flatness of 0.05 mm. Carrier pins are then adhesively secured over part of their area in a tolerance-free plane laterally into openings in the carrier element. On account of the extrusion and the finishing operation, tolerances accrue in the height dimension of the adhesively secured pins. In order to keep this height dimension within a margin of 0.05 mm in a card flat set, after the adhesion process a grading according to height dimensions is carried out. This process takes time and effort. Subsequently, the clothing strip is mounted on the heel face of the card flat bar in the described manner. Since the accumulation of the tolerances from the card flat bar, card flat clothing, offset occurring during mounting and from deformation as a result of tension when fitting on is too high, the above-described levelling by grinding is finally carried out across all the card flat bars. This involves grinding off up to 0.15 mm of material. The technological efficiency of the ground-down clothing tips is limited. If the clothing wire is over-ground, the actual operative sharpness in the region of the tip is taken away. In particular the accumulation of tolerances as the card flat clothing is assembled, the technically destructive grinding to a level finish and the decline in accuracy during use are therefore disadvantageous.
A card flat bar known from U.S. Pat. No. 4,827,573 comprises a steel tube pulled through a profiling mould. At both ends of the card flat bar there are solid head pieces, on which retaining elements for fixing a drive belt are mounted. These head pieces are joined to the card flat bar either by welding or with rivets or screws, so that they can be exchanged when they have become ineffectual as a result of wear. It has become apparent that the weld joints in some cases lead to stresses in the card flat bar and then exchange of the entire card flat bar is necessary. This same applies also to the screwed and riveted joint, that is, the joining force to be applied (turning the screw or the pressure involved in riveting) must be uniform to begin with and remain constant within a certain tolerance range for all card flat bars, in order to avoid undue compressive strain (i.e. a plastic deformation of the bar length by compression). Consequently, the height dimensions between slideway and clothing tips for all card flat bars of a card flat set are not equal. The known card flat bar has lateral walls that extend downwardly and parallel to a certain level and then converge. The end head piece consists of three elements, the head piece and the two-part holding element, which are arranged axially in relation to the carrier element. Only the head piece slides on the slideway, whereas the holding elements and the drive element are located away from the slideway. The drawback of this arrangement is that the drive element acting outside the slideway exerts an undesirable lever action, and hence a bending moment, on the head piece and on the carrier element. In addition, in this way the head piece does not slide with dimensional accuracy on the slideway, and disruptive tilting can occur. The manufacture of the carrier element from a steel tube, which is cold-drawn through a profiling mould and subsequently has to be heat-treated, is associated with considerable outlay, both in relation to manufacturing costs and from a technological point of view. Finally, it is particular disadvantage that the head pieces become worn during in operation. The effort involved in exchange of the worn head pieces is considerable, since the welded or riveted joints of the head pieces to the carrier element have to be unfastened and then reinstated again after the replacement. The repair can only be carried out when the carding machine is idle, which leads to considerable disruption to operations and to production losses.
It is an aim of the invention to produce a device of the kind described in the introduction that avoids or mitigates the said disadvantages, in particular in a simple manner renders possible a dimensionally stable and dimensionally accurate clothed card flat bar and allows simpler manufacture.